Geosynthetic Encasement Research Articles

3-Dimensional numerical analysis of geosynthetic double-encased annulus stone columns

A geosynthetic double-encapsulated annulus stone column technique is proposed in this study to overcome limitations associated with conventional stone columns, such as limited lateral load-bearing capacity and potential issues related to aggregate dispersion in soft soils. Geosynthetic double-encapsulated annulus stone columns are consistent with conventional stone columns besides being confined in and around the surrounding soil. The performance of geosynthetic double-encapsulated annulus stone columns is primarily dependent upon their outer-to-inner diameter ratio. For this reason, comprehensive 3-dimensional numerical studies were carried out to evaluate the optimum outer-to-inner diameter ratio of the annulus stone column. The results suggest that the ultimate load-carrying capacity of an annulus stone column increases with an increasing ratio of outer to inner diameter until an optimum value. In addition, the double encapsulation enhances confinement, improving shear stiffness and reducing lateral bulging. However, the load-carrying capacity was substantially reduced beyond the critical outer-to-inner diameter ratio. A simple analytical model extending the theory of thin cylinders is also introduced to estimate the accumulated stresses and strains in the geosynthetic encasement. The proposed model operates within a simplified framework of elastic solutions that facilitate practising engineers to design and optimize geosynthetic encasements for enhanced structural performance.

Numerical Stability Analysis of Sloped Geosynthetic Encased Stone Column Composite Foundation under Embankment Based on Equivalent Method

As an effective technology for the rapid treatment of soft-soil foundations, geosynthetic encased stone column (GESC) composite foundations are commonly used in various embankment engineerings, including those situated on sloped soft foundations. Nevertheless, there is still a scarcity of stability studies for sloped GESC composite foundations. Several 3D numerical models for sloped GESC composite foundations were established using an equivalent method. The influences of the area replacement ratio and the tensile strength of geosynthetic encasement on the stability were investigated. The results showed that the stability increased nonlinearly with the area replacement ratio, and there existed an optimal area replacement ratio (e.g., 24.56% in this study) to balance the safety and economic requirements. The stability increased linearly with the tensile strength of geosynthetic encasement at low tensile strength levels (lower than 105 kN/m in this study), and the impact was relatively limited compared with that of the area replacement ratio. In addition, the stability generally decreased nonlinearly as the foundation slope decreased, and high-angle (foundation slope close to 30°) sloped GESC composite foundations are recommended to be treated with multiple reinforcement techniques. The relationship between the minimum area replacement ratio and the foundation slope was further quantified by an exponential function, allowing for the determination of the area replacement ratio of various sloped GESC composite foundations and providing theoretical guidance for engineering practice.

Cyclic response of floating geosynthetic-encased steel slag columns in soft clay

Geosynthetic-encased stone column (GESC) technology for strengthening soft clay offers significant advantages in terms of cost-effectiveness, environmental sustainability, and engineering applicability. It is widely applied in treating soft foundations for railways, bridges, and embankments. This study evaluates the cyclic response of the geosynthetic-encased steel slag column (GESSC) composite foundation employing three-dimensional nonlinear finite element analysis. A numerical study is conducted to assess the cyclic response of floating GESSC considering the influence of key design variables, including cyclic load amplitude, loading frequency, geosynthetic encasement stiffness, and length-to-diameter ratio. Results show that both cyclic load amplitude and frequency affect the cumulative settlement and excess pore pressure within the GESSC foundation. Within specified limits, increasing the encasement stiffness and column length can significantly improve the GESSC load-bearing characteristics. The parametric study suggests an optimal geosynthetic encasement stiffness for the field prototype columns within the range of 4480–5760 kN/m and a critical steel slag column length of 10 times the column diameter.

Numerical Simulation of the Load Transfer Mechanism of a Geosynthetic Encased Stone Column Unit Cell under Embankment Loading

Numerical Simulation of the Load Transfer Mechanism of a Geosynthetic Encased Stone Column Unit Cell under Embankment Loading

Optimizing ground improvement with encased stone columns: a 3D numerical analysis in very soft clay

Purpose This study aims to investigate the behavior of different types of stone columns, including the short and floating columns, as well as the ordinary and the geosynthetic encased stone columns (OSC and GESC). The effectiveness of the geosynthetic encasement and the impact of the installation using the lateral expansion method on the column performance is evaluated through a three-dimensional (3D) unit cell numerical analysis. Design/methodology/approach A full 3D numerical analysis is carried out using the explicit finite element code PLAXIS 3D to examine the installation influence on settlement reduction (ß), lateral displacement (Ux) and vertical displacement (Uz) relative to different values of lateral expansion of the column (0% to 15%). Findings The findings demonstrate the superior performance of GESC, particularly short columns outperforming floating counterparts. This enhanced performance is attributed to the combined effects of geosynthetic encasement and increased lateral expansion. Notably, these strategies contribute significantly to decreasing lateral displacement (Ux) at the column’s edge and reducing vertical displacement (Uz) under the rigid footing. Originality/value In contrast to previous studies that examined the installation effect of OSC contexts, this paper presents a comprehensive investigation into the effect of geosynthetic encasement and the installation effects using the lateral expansion method in very soft soil, using 3D numerical simulation. The study emphasizes the significance of the consideration of geosynthetic encasement and lateral expansion of the column during the design process to enhance column performance.

Model tests on ordinary and geosynthetic encased stone columns with recycled aggregates as filler material

PurposeSincethe availability of natural aggregates is very sparse, recycled industrial and construction waste provides a sustainable alternative to ground improvement using vibro replacement method. Utilizing recycled building waste caters the requirement for its disposal and offers an effective remedy for the scarcity of natural resources. The aim of this study was to give a sustainable alternative for the natural aggregates as the material for stone column.Materials and methodsA good stone column material should be hard, dense, chemically inert and must comply with the size requirement. The utilization of construction debris and spent railway ballast as column material has been the subject of numerous researches. This work focuses on finding the suitability of railway ballast and concrete debris as alternatives for stone column material. A detailed laboratory testing of these materials has been carried to judge their strength requirements as the material for both Ordinary Stone Columns (OSCs) and Geosynthetic Encased Stone Columns (GESCs). The improvement in capacity of both OSCs and GESCs is evaluated by performing California Bearing Ratio (CBR) test in laboratory by creating unit cell stone column models of different recycled aggregates and comparing their load settlement behavior with natural aggregates.Results and discussionRailway ballast, natural aggregates, concrete debris and virgin soil were found to show decreasing order in CBR test results. Loading required for causing settlement in both OSCs and GESCsshowed remarkable increase as compared to that of virgin clay and the maximum load settlement improvement was observed for railway ballast in both the types of stone columns. The CBR values for GESC made from railway ballast, natural aggregates and concrete debris were 54, 49 and 38% respectively. On the other hand, CBR for OSC made from railway ballast, concrete debris and natural aggregates were found to be 25.5, 20.4 and 24% respectively and CBR of virgin clay was found to be just 11%.ConclusionThe demonstrated application of sustainable sources in place of natural aggregates provides a crucial pathway for utilizing the recycled aggregates as stone column filler material. Up on encasing the OSC with geotextile the performance of stone columns has improved appreciably in terms of load capacity. Railway ballast and concrete debris can be adopted as an alternate for the natural stone column materials to improve the bearing capacity of site consisting mainly of soft clays.

Shaking table tests on the influence of geosynthetic encasement stiffness on the shear reinforcement effect of GESC composite foundation

This paper presents an experimental study of shaking table tests on two geosynthetic encased stone columns (GESC) composite foundation models with different geosynthetic encasement stiffness to investigate the influence of geosynthetic encasement stiffness on the shear reinforcement effect. The reduced-scale GESC composite foundation models were designed according to the similitude relationships by scaling the model geometry, geosynthetic encasement stiffness, and input motions for shaking table tests in a 1 g gravitational field. The GESC composite foundation models were constructed using poorly graded sand, gravel, and geotextile encasement, and then were excited using a series of sinusoidal input motions with increasing peak acceleration. The acceleration amplification factors for the GESC composite foundation model with higher geosynthetic encasement stiffness are larger than those of the lower geosynthetic encasement stiffness model due to the increased stiffness of the composite foundation. The higher geosynthetic encasement stiffness composite foundation has smaller settlements and lateral displacements under the same input motions compared to the lower geosynthetic encasement stiffness composite foundation. The incremental geosynthetic encasement tensile strains increase with increasing input acceleration for both models. The longitudinal tensile effect of geosynthetic encasement plays an important role on the shear reinforcement mechanism of GESC.

Model test on bearing capacity of cemented slurry reinforced pile composite foundation

This study introduces the Geosynthetic Encased Prestressed (GEP) cemented slurry pile technology to address the challenges posed by waste slurry and dredged soil during infrastructure, urbanization, and underground space development. Laboratory model tests were conducted to assess the influence of prestress and geogrid on the bearing capacity of cemented slurry reinforced piles composited foundation. Results indicate that compared to non-geogrid pile composite foundations, both prestressed and non-geogrid pile composite foundations exhibited enhanced load-bearing capabilities in later stages, with an approximate increase of 25.89%. Additionally, the presence of geogrid effectively reduced settlement in the composite foundation under varying loads. The application of geogrid casings to seal cemented slurry reinforced piles facilitated load transfer downwards, restrained lateral expansion deformation, mitigated pile cracking, and bolstered bearing capacity. Consequently, a bearing capacity calculation equation for the composite foundation of cemented slurry reinforced piles was developed in this study. Parameter analysis demonstrated that higher geogrid tensile strength, smaller aspect ratio, greater cohesion, and internal friction angle of pile filler contributed to increased bearing capacity of cemented slurry reinforced piles. In summary, this study evaluates the viability of GEP cemented slurry piles and the impact of relevant parameters on pile bearing capacity of composite foundation. The findings offer valuable insights for practical engineering applications, advancement of eco-friendly transportation, and fostering sustainable development.

Use of Geosynthetic Encasement in Stone Column for Ground Improvement

Abstract: Ground improvement is an important requirement in today's construction industry as landreclamation is becoming increasingly popular. The stone column technique is a very efficient method of improving the strength parameters of soil like bearing capacity and reducing consolidation settlement. Soil reinforcement can be an ideal solution for the improvement of clay. Out of other conventional methods, stone columns are effectively being used for ground improvement, particularly for the construction of flexible structures such as road embankments, oil storage tanks, etc on soft soils. It offers a much more economical and sustainable alternative to piling and deep foundation solutions. This report investigates thequalitative and quantitative improvement of individual load capacity of stone columns by varying the diameterof stone columns through laboratory model tests conducted on stone columns installed in clay beds prepared in controlled conditions in a large-scale testing tank. The results from the load tests indicated the performance of a smaller diameter stone column is superior to that of a bigger diameter stone column and the stone grit used to Promote the vertical drainage function of the column by acting as a good filter.

Numerical Analysis of a Dual-Layer Geosynthetic-Encased Stone Column Installed in Soft Soil

Stone columns are being used to reduce soft soil settlement and increase load-carrying capacity. Since there is inadequate lateral support from the local native soil, soft soil undergoes excessive settlement under vertical loading. This issue is effectively resolved by suitably encasing stone column material by geosynthetic with significant axial stiffness, which provides the required additional confinement reported in the literature. In the current study, an effort has been made to examine the load settlement behaviour of the dual-layered geosynthetic-encased stone column (DL-GESC) under vertical loading. In order to simulate the behaviour of stone column-reinforced soft soil, a FEM analysis was performed using PLAXIS-3D and three-dimensional (3D) models made utilising the unit cell idealisation technique for a single column. The stone column diameter, spacing to diameter (s/d) ratio, and encasement layers were varied to determine their influence on load-settling behaviour. The vertical load-carrying capacity of the ground was significantly improved when an additional layer of geosynthetic encasement was inserted into the stone column as compared to SL-GESC. Improvement of 15–25% was observed for the analysis of a single column installed in soft clay, according to the result obtained. Improvement ratios have been discussed in detail for various encasement conditions.

Contribution of geosynthetic to the shear strength of geosynthetic encased stone columns

This paper presents a numerical study to evaluate the contribution of geosynthetic to the shear strength of geosynthetic encased stone column (GESC) under direct shear loading conditions. The backfill soil was characterised using the linearly elastic–plastic Mohr–Coulomb model. The geosynthetic encasement was simulated using linearly elastic liner elements. The interaction between the geosynthetic encasement and soils on both sides was modelled through two interfaces. The three-dimensional numerical model was validated using experimental data from direct shear tests of GESC models. The shear stress–strain response and the development of longitudinal and circumferential strains of GESC during the shear process were first discussed, and then a parametric study was conducted to investigate the effects of various design parameters on the shear strength of GESC and the contribution of geosynthetic. Results indicate that the shear resistance provided by the geosynthetic encasement develops slowly, which depends on the mobilisation of tensile strains. At the failure condition, the longitudinal strains are larger than the circumferential strains, which indicates that the longitudinal tensile rupture is more critical for GESC under shear loading. The vertical stress, geosynthetic encasement stiffness and stone column diameter and spacing have the most important influences on the shear strength contribution of geosynthetic encasement.

3-Dimensional Numerical Evaluation of Geosynthetic Encased Stone Columns in Unsaturated Soils

Geosynthetic encased stone columns are often designed using the conventional framework of saturated soils ignoring the influence of in-situ unsaturated soil conditions. This article evaluates the performance of stone columns with and without geosynthetic encasement extending the mechanics ofunsaturated soils. The focus of numerical simulations was directed towards understanding the influence of matric suction on the confining support offered by the surrounding soil to stone columns with and without geosynthetic encasement. Investigations were extended considering the stiffness and the length of the geosynthetic encasement. The numerical studies suggest the load-carrying capacity of stone columnincreased with an increase in the matric suction in the boundary effect and the primary transition zone. However, the contribution of matric suction towards load-carrying capacity starts reducing from the secondary transition zone. The information on boundary effect and transition zones can be derived fromthe soil-water characteristic curve, which is a relationship between the water content and soil suction. In addition, the effect of stiffness and length of encasing material in unsaturated soils was found to be in contrast with saturated soils. The results of the study are promising towards developing procedures thatcan be used in the rational design of stone columns in unsaturated soils.

Numerical Study on the Deformation Behavior of Geosynthetic-Encased Stone Columns Supporting Embankments

The method of encasing the stone column with a proper type of geosynthetic material is a widely used technique to provide the required lateral confinement and to avoid the dispersion of granular column material into soft clay. Along with the improved ultimate load capacity and the reduced settlement and bulging, the geosynthetic encasement preserves the easy drainage ability of stone columns. This paper presents the finite element analysis results of a hypothetical embankment on a soft soil deposit which is improved by geotextile encased stone columns and geogrid reinforced sand mat on top. At first, numerical results of three dimensional (3D) finite element model (FEM) were validated via the experimental data of previous field studies. Afterward, parametric studies were carried out on the FEM considering the effect of the sand mat thickness, the stiffness of the geosynthetic reinforcement, and the geosynthetic encasing length and encasement stiffness on both the horizontal and vertical deformation of stone columns. Settlement differences between columns and soft soil in both the short term and long term were also determined. The optimum values of sand mat layer thickness, vertical encasement length, and geosynthetic stiffness are recommended to be used for preliminary designs.

Shear performance of geosynthetic-encased stone column based on 3D-DEM simulation

The shear performance of the geosynthetic-encased stone column (GESC) is of significance to the stability analysis of increasingly used GESC improved foundations, since the toe of the embankment is generally affected by lateral loads. However, systematic studies in this field are still scarce now. In this paper, a three-dimensional discrete element method (3D-DEM) was employed to study the shear performance of the unit cell with a single GESC and the surrounding soil. The influences of some physical geosynthetic parameters (e.g., geogrid strength, encasement aperture and column diameter) on the shear performance were examined. Higher shear strength of GESC was observed when increasing the geogrid strength. The reinforcement effect of geosynthetic encasement increased with the column diameter non-linearly, however, the encasement aperture was found insignificant. The failure features of GESCs were considerably affected by the geogrid strength and can be generally divided into three categories (e.g., bulging failure, shear failure and flexural failure). Moreover, the shear load transfer mechanism and the development of the shear stress ratio were analyzed. Correlations between the shear strength parameter of GESC (e. g., apparent cohesion) and geogrid strength were quantified for practical use.

Sustainable utilisation of steel slag as granular column for ground improvement in geotechnical projects

Granular column is an attractive mitigation method which is widely used in geotechnical engineering to enhance the bearing capacity, reduce settlement and accelerate consolidation. Utilisation of industrial wastes such as steel slag in soil stabilization can be an environment-friendly and cost-effective extraction technique to the disposal of solid waste materials. Previous studies investigated the bearing capacity and settlement of ground improved with granular columns with or without the geosynthetic encasement. However, very limited number of studies have investigated the response of ordinary stone columns without encasement and geosynthetic encased steel slag columns under lateral loading. In this paper, the lateral load capacity of steel slag granular column-soil composites has been investigated. For this purpose, a series of large direct shear tests were performed on the column-soil composites with the steel slag column and the ordinary stone column with or without the geosynthetic encasement. The effect of type of column materials (steel slag and sand), column diameter, number of columns, columns arrangement, and geosynthetic encasement on the shear strength parameters of column-soil composites have been studied. The experimental results show the effectiveness of using the steel slag columns to improve the lateral load-bearing performance of soil.

Influence of positions of the geotextile on the load-settlement behaviour of circular footing resting on single stone column by 2D Plaxis software

Purpose: This study aims to study the load – settlement behaviour of circular footing rested on encased single stone column. Design/methodology/approach: The effect of vertical, horizontal and combined verticalhorizontal encasement of stone column on the load carrying capacity were examined numerically. The effect of stone column dimension (80 mm and 100 mm), length (400 mm and 500 mm), and spacing of reinforcement on the load carrying capacity and reinforcement ratio were assessed. Findings: The obtained results revealed that the load carrying capacity of geotextile encased stone columns are more than ordinary stone columns. For vertically encased stone columns as the diameter increases, the advantage of encasement decreases. Whereas, for horizontally encased stone column and combined vertical- horizontal encased stone column, the performance of encasement intensifies as the diameter of stone column increases. The improvement in the load carrying capacity of clay bed reinforced with combined verticalhorizontal encased stone columns are higher than vertical encased stone columns or horizontal encased stone column. The maximum performance of encasement was observed for VHESC1 of D = 80 mm. Research limitations/implications: For this study, the diameter of footing and stone column was kept same. The interface strength factor between stone column and clay bed was not considered. Practical implications: The encased stone column could be use improve the laod bearing capacity of weak soils. Originality/value: Many studies are available in literature regarding use of geosynthetic as vertical encasement and horizontal encasement of stone column. The study on combined effect of vertical and horizontal encasement of stone column on load carrying capacity of weak soil is very minimal. Keeping this in view, the present work was carried out.

Utilisation of steel slag as a granular column to enhance the lateral load capacity of soil

ABSTRACT Granular columns are widely used to enhance the bearing capacity of weak soil. The filling material of columns is generally stone, gravel or sand. The use of industrial wastes such as steel slag in civil engineering applications not only reduces environmental pollution, but also leads to cost benefits. So far, many studies have been done on the behaviour of granular columns with and without geosynthetic encasement under vertical loads; however, very limited studies were conducted on the behaviour of waste granular columns with and without geosynthetic encasement under lateral loads. Therefore, this study aims to evaluate the lateral load capacity of steel slag granular columns reinforced with geosynthetic using a large direct shear test apparatus. Results demonstrated that the use of steel slag column improved the lateral load capacity of soil. The use of geosynthetic encasement in floating steel slag column could significantly enhance both the peak and critical state shear strength. The results indicated the viability of using steel slag column as a soil reinforcement providing sustainable and technical benefits mainly when using geosynthetic reinforcement.

Deformation behaviour of granular column reinforced by geosynthetic encasement

In Vietnam, the overpopulation and strong economic development require the synchronous development of infrastructure such as roads, urban areas, industrial parks, export processing zones, etc. With such requirements, the development of land fund for infrastructure construction is an indispensable need. Meanwhile, the appropriate land fund is very limited. Therefore, the land fund must be developed for areas with little value for agriculture, such as swamps, estuaries, and coastal areas, etc. These areas often have weak geological conditions; hence, to meet the requirements of infrastructure construction on the soft ground, it is necessary to carry out soil improvement to ensure load bearing capacity, total settlement, and consolidation settlement but still ensuring economic effectiveness. Beside several conventional methods widely used for soft soil improvement in order to increase bearing capacity and accelerate consolidation settlement of the ground, geosynthetic reinforced granular column is one of the new methods that has been applied to improving soft ground in designing practice in the recent years due to the many advantages of this method compared with other methods. In this paper, based on the unit cell model, the authors research on deformation behavior of granular column reinforced by geosynthetic encasement through the analytical analysis by varying external loadings corresponding to column diameter, stiffness of geosynthetic encasement. The settlements of a single geosynthetic encased granular column and load bearing capacity of the composite foundation are calculated on geological conditions of Ash Pond Area of Song Hau 1 Thermal Power Plant located in Hau Giang Province. The relationship between settlement and load bearing capacity with external loadings for different column diameters and geosynthetic stiffnesses are shown schematically. Other considerations related to factor of safety are also presented. The future researches are also proposed.

Settlement of Geosynthetic Encased Stone Columns Liquefaction Condition in Box Culvert

When the box culvert system is placed on a sandy soil layer with a relatively low bearing capacity and is disposed to potential liquefaction, the soil layer must be repaired to avoid damages to the box culvert structure. The proposed method is Geosynthetic Encased Stone Columns (GESC) to increase the bearing capacity and anticipated the liquefaction potential. however, to meet the criteria for a stable and safe GESC soil improvement in liquefaction conditions, the value of the settlement must meet the requirements for the settlement permit limit. This research was conducted to determine the potential for liquefaction at the study location, to calculate the value of single and group settlements in liquefaction conditions and to analyze the stability of single and group settlements including safe or unsafe in liquefaction conditions. Analysis of liquefaction potential was analyzed based on SPT data using the Valera and Donovan method, and settlement analysis applied the Almeida and Alexiew method. The analysis shows that potential liquefaction due to an earthquake with a magnitude of 9.0 SR will be at a depth of 4 to 8 m. Single and group settlements (144 sets) with an installation distance of 1.2 m with a diameter of 0.4 m and at a depth of 10 m are 246.23 and 214.92 mm, respectively. The entire GESC system is considered to be in an unstable and unsafe condition against potential liquefaction and box culvert loading.

Influence of encasement length and geosynthetic stiffness on the performance of stone column: 3D DEM-FDM coupled numerical investigation

The design of geosynthetic encasement is the most important factor that controls the performance of the geosynthetic-encased stone column (GESC) improved ground, and encasement length (Lenc) and geosynthetic stiffness (J) are two basic design items. Numerous continuum-based numerical models have been proposed to investigate the influence of geosynthetic encasement on the behavior of GESC improved ground, however, the micro-mechanics of stone aggregates cannot be properly simulated due to its discrete nature. In this paper, a three-dimensional discrete element method (DEM) and the finite difference method (FDM) coupled numerical modeling scheme was proposed. Surrounding clay is modeled by the continuum method using FLAC3D and the stone column and geosynthetics are modeled by the discrete element method using PFC3D. The proposed numerical models are validated using laboratory observations. The influence of geosynthetic encasement is analyzed by predicting pressure-settlement behavior, lateral deformation of surrounding clay, stress distribution within the column, and microscopic characteristics of granular materials (i.e., porosity, coordination number and contact force distribution). Numerical results demonstrate that full length and high stiffness encasement will significantly improve the load-bearing capacity of GESCs. In practice, fully-encased stone columns are recommended for reducing the settlement.